Shivaram P, et al. - Researchers tested the premise that, in children, increased venous compliance manifested as inferior vena cava (IVC) dilation is an important syncope substrate. In 191 children and adolescents with syncope and 95 controls, IVC diameters were measured. They divided subjects according to age <12 years (younger group) and ≥12 years (older group). Relationships have been assessed between indexed inferior vena cava (iIVC) and the time of day. Compared to controls, the IVC in teenagers with syncope is enlarged, implying that venous capacitance and the pooling that results play roles in syncope pathogenesis. IVC dilation is not seen in younger children with syncope, which infers another mechanism causes syncope in these patients.